Western water hemlock
Discuss this plant with the guide — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.
Cicuta douglasii
Native wetland hazard; not an A/B/C listing in the reviewed rule. C-wetland-guide CO-rules-2025
Potentially fatal poisoning; wetland look-alike danger. Exposure help.
Identification caveat: The older Colorado wetland guide treats C. douglasii within C. maculata var. angustifolia. The photos and Utah source identify C. douglasii. This is separate from poison hemlock (Conium maculatum). Older home-treatment instructions and an incorrect chemical classification in sources are excluded.
Still researching this plant
This is a sourced working profile. Evidence is incomplete for Dogs & cats. Identification and source-photo limits are explained below. Independent botanical and veterinary review is pending. Uncertainty is not a finding that the plant is safe.
Three views of this plant
Source-identified reference photographs; these are not a complete identification key. A source location outside Colorado does not establish local occurrence.
Lee Cain · CC BY 4.0
Photo source and identification
Original record · Original image
Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Matt Berger · CC BY 4.0
Photo source and identification
Original record · Original image
Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
N5jrn · CC BY-SA 4.0
Photo source and identification
Original record · Original image
Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Recognize
A wetland perennial with clusters of small white flowers and divided leaves; veins terminate in notches between the leaflet teeth. Never taste, cut roots or use this short description as a foraging test. U-water-hemlock
Plants & habitat
Occurs around wet ground, ditches and waterways. Colorado floras have used broader Cicuta names for related populations. C-wetland-guide
Evidence scope: Older regional flora; taxonomic scope differs.
People
Routt County identifies water hemlock as a potentially lethal poison. Treat suspected ingestion as an emergency. C-routt-guide
Dogs & cats
The county guide explicitly warns about dogs. Cat-specific clinical detail is not established here; keep all pets away from chewing plants or exposed roots. C-routt-guide
Evidence scope: Dog warning; cat evidence gap.
Other animals
Highly poisonous to livestock, especially the roots. Convulsions and death can follow ingestion. U-water-hemlock
Before taking action
Confirm identification and the requirements of your county weed program. For chemical treatment, follow the current product label, including restrictions around animals and water. S27
References
- C-wetland-guide — Common Wetland Plants of Colorado’s Western Slope, Colorado Natural Heritage Program / Colorado State University. Accessed 2026-09-07T01:14:13+00:00. Locator: Water hemlock and western poison ivy entries; taxonomic scope.
- CO-rules-2025 — Colorado Noxious Weed Act rules, 8 CCR 1206-2, Colorado Secretary of State / Department of Agriculture. Accessed 2026-09-07T01:07:48+00:00. Locator: Parts 3.1, 4.1, 5.1; management provisions; effective May 15, 2025.
- U-water-hemlock — Water Hemlock, Utah State University Extension. Accessed 2026-09-07T01:14:00+00:00. Locator: Cicuta douglasii identification and toxicity.
- C-routt-guide — Routt County Weed Identification Guide, Routt County / Colorado State University Extension. Accessed 2026-09-07T01:14:14+00:00. Locator: Common weeds and poisonous plants; 2021 edition.
- S27 — 2103 – Colorado Noxious Weeds, PlantTalk Colorado · CSU Extension. Accessed 2026-09-07T00:23:57+00:00. Locator: List A, B and C management categories.